System for controlling ultrasonic clamping and cutting instruments

ABSTRACT

A control system for use with an ultrasonic surgical instrument includes a generator supplying electrical energy to an ultrasonic surgical instrument, the electrical energy supplied by the generator being controlled such that power applied by the instrument is maintained constant once a predetermined pressure threshold is met. The control system operates by assigning a nominal power at which the ultrasonic instrument is to operate and adjusting the current and voltage applied to the ultrasonic surgical instrument so as to maintain the power applied by the ultrasonic surgical instrument at approximately the nominal power.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to ultrasonic surgical clamping and cuttinginstruments. More particularly, the invention relates to an improvedpower limiting mechanism for ultrasonic surgical cutting and clampinginstruments.

2. Description of the Prior Art

Ultrasonic instruments are used for the safe and effective treatment ofmany medical conditions. Ultrasonic instruments are advantageous becausethey may be used to cut and/or coagulate organic tissue using energy inthe form of mechanical vibrations transmitted to a surgical end-effectorat ultrasonic frequencies.

Ultrasonic vibrations, when transmitted to organic tissue at suitableenergy levels and using a suitable end-effector, may be used to cutand/or dissect tissue. Ultrasonic instruments utilizing solid coretechnology are particularly advantageous, because of the amount ofultrasonic energy that may be transmitted from the ultrasonic transducerthrough the waveguide to the surgical end-effector. Such instruments areparticularly suited for use in minimally invasive procedures, such as,endoscopic or laparoscopic procedures, where the end-effector is passedthrough a trocar to reach the surgical site.

Ultrasonic vibration is induced in the surgical end-effector by, forexample, an electrically excited transducer that may be constructed ofone or more piezoelectric or magneto-resistive elements in theinstrument handpiece. Vibrations generated by the transducer aretransmitted to the surgical end-effector via an ultrasonic waveguideextending from the transducer section to the surgical end-effector.

Many such ultrasonic surgical instruments are known within the priorart. However, they are highly responsive to the pressure applied by thesurgeon. In particular, as the surgeon applies greater pressure, thevibration characteristics of the ultrasonic instrument are altered. Infact, in situations where a surgeon exceeds a predetermined pressurelevel, the power delivered to the tissue may be too high. This mayresult in undesired tissue effects, such as poor hemostasis oftransacted vessels. Furthermore, it is possible that the surgicalinstrument might not be equipped to handle the material stressrequirements for producing the vibration levels at the high pressurelevels, thus resulting in undesirable operation of the instrument.Attempts have been made to remedy problems associated with theapplication of different pressures, for example, by the inclusion ofsprings within the actuation assembly to mechanically attempt to controlapplied pressure. However, these attempts have been met with onlylimited success.

As such, a device is needed wherein a constant power profile is achieveddespite personal preferences in the force applied by the surgeon. Thepresent invention provides such a device.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide acontrol system for use with an ultrasonic surgical instrument. Thecontrol system includes a generator supplying electrical energy to anultrasonic surgical instrument, the electrical energy supplied by thegenerator being controlled such that power applied by the instrument ismaintained constant once a predetermined pressure threshold is met.

It is also an object of the present invention to provide an ultrasonicsurgical system. The ultrasonic surgical system includes an instrumentand an ultrasonic signal generator linked to the instrument forsupplying a desired signal to the instrument. The instrument includes anultrasonic transducer, a housing and an end effector. The ultrasonicsignal generator includes a control system. The control system includesa generator supplying electrical energy to the instrument, theelectrical energy supplied by the generator being controlled such thatpower applied by the instrument is maintained constant once apredetermined pressure threshold is met.

It is another object of the present invention to provide a method forcontrolling the application of power by an ultrasonic surgicalinstrument. The method is achieved by assigning a nominal power at whichthe ultrasonic instrument is to operate and adjusting the current andvoltage applied to the ultrasonic surgical instrument so as to maintainthe power applied by the ultrasonic surgical instrument at approximatelythe nominal power.

Other objects and advantages of the present invention will becomeapparent from the following detailed description when viewed inconjunction with the accompanying drawings, which set forth certainembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the system in accordance with the present invention.

FIG. 2 is a graph showing the current, voltage and power profilescontemplated in accordance with the present invention.

FIG. 3 is a flow chart of a preferred technique for controlling thepower level applied to an ultrasonic instrument in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed embodiment of the present invention is disclosed herein. Itshould be understood, however, that the disclosed embodiment is merelyexemplary of the invention, which may be embodied in various forms.Therefore, the details disclosed herein are not to be interpreted aslimited, but merely as the basis for the claims and as a basis forteaching one skilled in the art how to make and/or use the invention.

With reference to FIG. 1, an ultrasonic system 10 for use in conjunctionwith ultrasonic surgical clamping and cutting instruments 12 isdisclosed. In accordance with a preferred embodiment of the presentinvention the ultrasonic system 10 includes an ultrasonic signalgenerator 15 adapted for applying current and voltage sufficient tomaintain power substantially constant during the procedure.

In accordance with a preferred embodiment of the present invention, thesystem is adapted for working with an ultrasonic instrument 12 similarto that disclosed in U.S. Pat. No. 6,458,142, entitled “Force LimitingMechanism for an Ultrasonic Surgical Instrument”, which is incorporatedherein by reference, although the force limiting mechanism of thisinstrument is not needed in view of the present invention's use ofvoltage and current in controlling the power applied by the instrument.While a preferred instrument is disclosed in accordance with describingthe present invention, those skilled in the art will appreciate that thegoal of the present invention is to provide a system adapted for usewith a wide range of devices.

For the purpose of disclosing the present invention, the instrument 12includes sandwich type ultrasonic transducer 82, a handpiece housing 20and a clamp coagulator 120. The clamp coagulator 120 is used for open orlaparoscopic surgery. The ultrasonic transducer 82, which is known as a“Langevin stack”, generally includes a transduction portion 90, a firstresonator or end-bell 92, a second resonator or fore-bell 94, andancillary components. An acoustic assembly 80 includes the ultrasonictransducer 82, mount 36, velocity transformer 64 and surface 95.

The distal end of the end-bell 92 is connected to the proximal end ofthe transduction portion 90, and the proximal end of the fore-bell 94 isconnected to the distal end of the transduction portion 90. Thefore-bell 94 and end-bell 92 have a length determined by a number ofvariables, including the thickness of the transduction portion 90, thedensity and module of elasticity of the material used to manufacture theend-bell 92 and fore-bell 94 and the resonant frequency of theultrasonic transducer 82. The fore-bell 94 may be tapered inwardly fromits proximal end to its distal end to amplify the ultrasonic vibrationamplitude as a velocity transformer (not shown) or, alternately, mayhave no amplification.

The piezoelectric element 100 is preferably manufactured from anysuitable material, such as, for example, lead zirconate-titanate, leadmeta-niobate, lead-titanate, or other piezoelectric crystal materials.Each of the positive electrodes 96, negative electrodes 98 andpiezoelectric elements has a bore extending through the center thereof.The positive and negative electrodes 96, 98 are electrically coupled tofirst and second wires 102, 104 respectively. The first and second wires102, 104 are encased within a cable 25 and electrically connectable tothe ultrasonic signal generator of the ultrasonic system 10.

In practice, the ultrasonic transducer 82 of the acoustic assembly 80converts the electrical signal from the ultrasonic signal generator intomechanical energy that results in primarily longitudinal vibratorymotion of the ultrasonic transducer 82 and an end-effector 180 at anultrasonic frequency. When the acoustic assembly 80 is energized, avibratory motion standing wave is generated through the acousticassembly 80. The amplitude of the vibratory motion at any point alongthe acoustic assembly 80 depends on the location along the acousticassembly 80 at which the vibratory motion is measured.

The first and second wires 102, 104 transmit electrical signals from theultrasonic signal generator 15 to positive electrodes 96 and negativeelectrodes 98. A suitable generator is available as model number GEN01,from Ethicon Endo-Surgery, Inc., Cincinnati, Ohio. The piezoelectricelements 100 are energized by an electrical signal supplied from theultrasonic signal generator in response to a foot switch 118 to producean acoustic standing wave in the acoustic assembly 80. The electricalsignal causes disturbances in the piezoelectric element 100 in the formof repeated displacements resulting in large compression forces withinthe material. The repeated small displacements cause the piezoelectricelements 100 to expand and contract in a continuous manner along theaccess of the voltage gradient, producing longitudinal waves ofultrasonic energy. The ultrasonic energy is transmitted through theacoustic assembly 80 to the end-effector 180.

In order for the acoustic assembly 80 to deliver energy to theend-effector 180, all components of the acoustic assembly 80 must beacoustically coupled to the ultrasonically active portions of the clampcoagulator 120. The distal end of the ultrasonic transducer 82 may beacoustically coupled at a first surface to the proximal end of theultrasonic waveguide by a threaded connection, such as a stud 50. Thecomponents of the acoustic assembly 80 are preferably acoustically tunedsuch that the length of any assembly is an integral number of one halfwave lengths, where the wavelength lambda is the wavelength of apre-selected or operating longitudinal vibration drive frequency of theacoustic assembly 80 and where N is any positive integer. It is alsocontemplated the acoustic assembly 80 may incorporate any suitablearrangement of acoustic elements without departing from the spirit ofthe present invention.

In an effort to accommodate different force profiles utilized bydifferent surgeons, the present invention controls the power applied bythe ultrasonic surgical generator 15 to the instrument 12. The appliednominal power is controlled in an effort to prevent undesired effects tothe tissue being clamped and/or cut. By controlling power in accordancewith the present invention, the need for mechanical control systemsfound in prior art ultrasonic instruments is eliminated and improvedfeedback is provided to the user. Ultimately, the power applied via anultrasonic instrument 12 is affected by the friction generated betweenthe tissue and the end-effector 180, the velocity of the end-effectorand the normal force applied by the end-effector 180. In practice, thefriction between the tissue and the end-effector 180 is generally prettyconstant with only slight changes due to the dryness of the tissue. Thevariables in power application are, therefore, the velocity of theend-effector and the applied normal force.

As will be discussed below in detail, the present invention maintains asubstantially constant power input by controlling the voltage andcurrent utilized by the ultrasonic surgical instrument 12 based upon themeasured impedance through the transducer 82 as it relates to thedesired nominal power level. In particular, and with reference to thepower profile shown in FIG. 2, the power applied by the ultrasonicsurgical instrument 12 is maintained constant after a predeterminedpressure level is reached. By continually monitoring the impedancethrough the transducer 82, which relates to the force being applied bythe operator, and adjusting the current passing therethrough, whichrelates to the velocity of the end-effector 180, such that the nominalpower is maintained at a desired level, the present invention is able toprovide for a consistent application of power to tissue regardless ofthe force applied by the operator.

The power produced by the ultrasonic surgical instrument 12 is theproduct of the voltage and current utilized by the ultrasonic surgicalinstrument 12 and provided by the ultrasonic surgical generator 15. Atforce levels applied by the surgeon below 400 grams as shown in FIG. 2,the ultrasonic surgical generator 15 is designed to maintain a certainfixed vibration velocity level at the end effecter 180 of the ultrasonicinstrument 12 by maintaining the input current to the transducer. Assuch, the voltage supplied by the ultrasonic surgical generator 15 ofthe ultrasonic surgical instrument 12 is proportionally increased as theforce applied by the surgeon continues to increase, thereby maintaininga fixed current. As a result, the power up to the 400 grams point inFIG. 2 is increasing continuously. Beyond the 400 grams point, theultrasonic surgical generator 15 is designed to switch to a mode inwhich it maintains a certain fixed power into the scalpel and therebyinto the target tissue regardless of the force applied by the operator.The voltage while in this mode is increased in such proportion whichresults in decrease in current as the force applied by the surgeon isincreased, but the power is maintained at the same level.

The reduction in current due to varying the proportion by which thevoltage is increased results in decreased current flowing thorough thetransducer 82 of the ultrasonic surgical instrument 12 and therebydecreased vibration velocity of the end-effecter 180 of the ultrasonicinstrument 12. In contrast to prior devices, the voltage is notincreased in a manner which will maintain the current, and consequentlythe vibrations, at a constant level. Rather, the voltage is increased inrelation to the current such that the power supplied through theultrasonic transducer 82 of the ultrasonic surgical instrument 12 ismaintained at a constant level. The mechanism for maintaining constantpower is achieved by controlling voltage and current, in considerationof the applied force, so as to maintain a constant nominal power. Bymaintaining power at a constant level, regardless of the applied force,by controlling the voltage and current passing through the ultrasonicsurgical instrument 12, the present ultrasonic instrument 12 will applyconsistent power regardless of the pressure applied by the surgeon.

As such, and as discussed above, the application of constant power inaccordance with the present invention balances vibration (or velocity)levels of the end-effector 180 with the normal pressure applied by theend-effector 180. For example, when a surgeon applies greater normalforce via the end-effector 180, the vibration level is reduced and theapplied power level remains constant. As those skilled in the art willappreciate, and with reference to the graph presented in FIG. 2, acertain period of ramping up is necessary for utilization of the presentsystem in conjunction with ultrasonic surgical instrument 12. As shownin the FIG. 2, the ramp up occurs as the pressure increases from zerograms force to 400 grams force. During this time, the current ismaintained constant while the voltage increases to compensate for thetendency for a reduction in vibrations, and thus current, as the forceapplied by the surgeon increases.

Once a force of 400 grams is achieved, the voltage and current areregulated to maintain the power at a constant level. As those skilled inthe art will appreciate, the power is maintained constant within theforce characteristics contemplated for use in accordance with thepresent invention. The application of force beyond the predeterminedlimits will result in malfunctioning of the device and surgeons will bewarned that an unacceptable force level has been reached.

More particularly, and with reference to FIG. 3, a flow chart presentinga preferred operating procedure is disclosed. In accordance with thepresent invention, the ultrasonic surgical instrument 12 and theultrasonic surgical generator 15 are started. The ultrasonic surgicalgenerator 15, via its operating processor, reads the nominal drive setpoints from a memory device embedded in the ultrasonic instrument 12. Inparticular, the following set points are read: the drive current at noload (that is, the nominal current I_(nom)) and the nominal power(P_(nom)) to regulate to across the load (that is, the predeterminedpower at which the instrument is designed for operation in accordancewith the present invention).

Thereafter, it is determined whether instrument activation has beenrequested by the operator. If the answer is NO, the instrument 12returns to activation requested status awaiting a request foractivation. If activation of the instrument is requested by theoperator, a frequency sweep is performed to locate resonance frequenciesof the instrument 12 and to attempt driving the instrument at nominalcurrent (I_(nom)). The ultrasonic surgical generator 15 then determineswhether the resonance frequency is located and whether the instrument iscapable of being driven at nominal current (I_(nom)). If the ultrasonicsurgical generator 15 fails to either locate the resonance frequency ordrive the scalpel at nominal current (I_(nom)), an error is indicatedand the ultrasonic surgical generator 15 shuts down. If the resonancefrequency is located and the instrument operates at nominal currentlevels (I_(nom)), the scalpel impedance (Z_(r)) at the resonancefrequency is calculated. This is achieved utilizing the followingformula:Z _(r) =V÷I

where,

-   -   I=drive current (which is initially I_(nom)), and    -   V=drive voltage required to achieve drive current.

The system then determines whether the power, calculated as I²×Z_(r) isgreater than the nominal power (P_(nom)) to regulate across the load. Ifit is determined that the nominal power (P_(nom)) to regulate across theload is less than I²×Z_(r), the power being applied by the instrument isconsidered to be too high and the instrument power is reduced to nominalpower (P_(nom)) by reducing the drive current to I=SQRT (P_(nom)/Z_(r)).As those skilled in the art will appreciate, the drive current is simplyadjusted by altering the drive voltage.

Thereafter, the ultrasonic surgical generator 15 determines whether itis able to maintain the lock on the resonance frequency and to drive atthe desired current. If the answer is NO, an error is indicated and theprocedure ends. If the ultrasonic surgical generator is able to maintaina lock on the resonance frequency and drive at the desired current, theultrasonic surgical generator 15 checks to see if a deactivation requestis detected, and if no deactivation request is detected, the ultrasonicsurgical generator 15 returns to the step of calculating the scalpelimpedance (Z_(r)) at the resonance frequency.

If the nominal power (P_(nom)) is greater than I²×Z_(r), the nominaldrive current (I_(nom)) is maintained and the system determines whetherit is able to maintain a lock on the resonance frequency and the driveat the desired current. If the answer is NO, an error is indicated andthe procedure ends. If the answer is YES, the ultrasonic surgicalgenerator 15 determines whether any deactivation requests have beendetected, and if none are detected, the ultrasonic surgical generator 15returns to the step of calculating the scalpel impedance (Z_(r)) at theresonance frequency.

This procedure is continually repeated during the surgical procedure tomaintain a nominal desired power level and to operate the system inaccordance with the present invention. By continually monitoring theimpedance through the transducer 82, which relates to the force beingapplied by the operator, and adjusting the current passing therethrough,which relates to the velocity of the end-effector 180, such that thenominal power is maintained at a desired level the present invention isable to provide for a consistent application of power regardless of theforce applied by the operator.

While the preferred embodiments have been shown and described, it willbe understood that there is no intent to limit the invention by suchdisclosure, but rather, is intended to cover all modifications andalternate constructions falling within the spirit and scope of theinvention.

1. An ultrasonic surgical system, comprising: an instrument and anultrasonic signal generator linked to the instrument for supplying adesired signal to the instrument, the instrument includes an ultrasonictransducer, a housing and an end-effector; the ultrasonic signalgenerator includes a control system, the control system includes agenerator supplying electrical energy to the instrument, the electricalenergy supplied by the generator being controlled such that powerapplied by the instrument is maintained constant once a predeterminedpressure threshold is met.
 2. The ultrasonic surgical system accordingto claim 1, wherein the power applied by the instrument is equal to theproduct of the current and voltage generated by the generator.
 3. Theultrasonic surgical system according to claim 2, further including meansfor measuring impedance passing through the instrument and controllingthe power level based upon the measured impedance.
 4. The ultrasonicsurgical system according to claim 3, wherein the means for controllingthe power level includes adjusting current passing through theinstrument based upon the measured impedance.
 5. The ultrasonic surgicalsystem according to claim 1, wherein voltage supplied by the generatoris increased as the force applied continues to increase.
 6. Theultrasonic surgical system according to claim 3, further including meansfor measuring impedance passing through the instrument and controllingthe power level based upon the measured impedance.
 7. The ultrasonicsurgical system according to claim 6, wherein the means for controllingthe power level includes adjusting current passing through theinstrument based upon the measured impedance.
 8. The ultrasonic surgicalsystem according to claim 1, further including means for balancingvibration levels of the instrument with pressure applied by theinstrument.